Low frequency inertia-type pickup



March 20, 1962 S. KARPCHUK LOW FREQUENCY INERTIA-TYPE PICKUP Filed Oct.

INVENTOR 0 MMM ATTORNEYS United States PatentO 3,026,429 LOW FREQUENCY INERTIA-TYPE PICKUP Sylvester Karpchuk, Philadelphia, Pa., assignor to Tinius Olsen Testing Machine Company, Willow Grove, Pa., a corporation of Pennsylvania Filed Oct. 28, 1959, Ser. No. 849,219 6 Claims. (Cl. 310-25) This invention relates to vibration pickups and in particular relates to improvements in such pickups which adapt the same for use in both high and very low frequency ranges.

In my Patent 2,946,218, I have disclosed a tunable vibration pickup comprising a coil element and a permanent magnet which is suspended by a pair of springs which provide for relative motion between the coil and the magnet, the motion developing a signal or voltage in the coil. Means are provided for varying the elfective vibrating lengths of the springs so that the pickup can be tuned to resonant frequency of the part with which it is being used.

While the pickup described above is designed for use over a broad band frequency range, the present invention provides for improvements in the same, particularly in extending use at very low frequency. In general, this is accomplished by mounting magnetic material over the magnet, the magnetic material being characterized by three sections, the interaction of which, with the poles of the magnet, provide for highly accurate and desirable operation at low frequencies and yet does not interfere with operation at the higher frequencies.

While in the pickup of my Patent 2,946,218 a pair of springs are used for suspending the magnet, the invention contemplates the use of a tunable single spring for suspending the magnet with a magnetic material mounted over the magnet and having three sections which interact with the magnet to produce the desired effect for low frequency operation.

The manner in which the invention is constructed will be apparent from the following description and drawings wherein:

FIGURE 1 is a vertical section of a two-spring tunable pickup incorporating the invention;

FIGURE 2 is a plan section taken along the lines 22 of FIGURE 1;

FIGURE 3 is an isometric view of an assembly having magnetic material provided with three sections;

FIGURE 4 is an isometric view of a magnet assembly;

FIGURE 5 is a vertical section of a single spring tunable pickup incorporating the invention; and

FIGURE 6 is a plan view of the magnetic material used in the pickup of FIGURE 5.

In FIGURE 1 the numeral 1 designates the housing of the unit which is constructed similarly as shown in my above-mentioned Patent 2,946,218 except for certain differences which will appear later. Secured to the top of the housing are a pair of strip-like springs 2 and 3 which are connected to a spacer 4 on which is mounted the magnet 5. A screw 6 is rotatably mounted on the housing and is connected to a knob 10 by means of which the screw can be rotated. A nut 11 slidably mounted in the housing for up and down movement has slots which slidably interengage the springs 2 and 3. The out is also connected to the screw 6. When the knob 10 is rotated the nut will be moved up or down depending on the rotation of the screw. The effect of this is to vary the effective vibrating lengths of the springs 2 and 3, i.e., the parts of the springs which are below the nut. On the bottom of the housing is the coil assembly 12 which is preferably the air-core type. The non-magnetic insert 13 extends through the aperture in the coil and is fixed to the housing 1 so as to secure the coil assembly in position.

ICC

The springs 2 and 3 provide for relative motion as between the magnet and coil and this motion takes place in a vertical plane, for example, the plane P indicated in FIGURE 2. When the device is placed upon a member which is not vibrating the magnet and coil will assume the position as shown in FIGURE 1. For descriptive purposes this is termed the neutral position. With vibration the magnet may move from the neutral position to the left and then back to the neutral position and thence to the right and back to neutral to complete a full cycle of vibration. It will be understood of course, that in certain instances the magnet may, for all practical purposes, remain motionless while the frame and coil vibrate from neutral to the left and to the right. This, of course, produces the same effect as movement of the magnet.

The springs 2 and 3, the spacer 4 and the securing screws all are preferably made of non-magnetic material.

Just above the magnet 4 there is mounted a frame 16. As shown in FIGURE 3 the frame 16 is rectangular in shape and provided with ears 20 by means of which it is attached to the housing 1. The housing is provided with a plurailty of slots 21 through which extend the screws 22. By loosening the screws the frame 16 may be adjusted in a vertical direction and fixed in the desired adjusted position. The frame 16 and screws 20 are preferably of non-magnetic material.

The frame 16 carries the magnetic material 23 which may be secured to the same as by non-magnetic rivets 24. As indicated, the magnetic material has a central section 25 and two outboard sections 26 and 27.

The manner in which the magnetic material 23 effects operation of the magnet will be explained following. Assume first that the magnet is in the neutral position or as shown in FIGURE 1 and that the left-hand side is a north pole N and the right-hand side is a south pole S. The lines of flux from the magnet will cause the outboard section 26 to become a south pole and the outboard section 27 to become a north pole. The central section 25 will, for all practical purposes, be unpolarized. If the magnet is moved from the neutral position toward the right-hand side, the section 25 becomes a south pole and the section 27 becomes a stronger north pole. As the magnet starts to move toward neutral position, the repulsion between the south pole of the magnet and the south pole 25 tends to slow down the magnet. As the magnet approaches the neutral position the section 25 begins to change from south to north polarity and as the magnet passes just beyond the neutral position the center section 25 is completely reversed in polarity. As the magnet continues to move to the left the section 26 becomes a stronger south pole and the center section 25 becomes a stronger north pole. As the magnet moves back to neutral, the north pole of the magnet and north pole 25 repel and this tends to slow down the magnet.

In connection with the motion of the magnet from neutral to one side, say to the left side, it will be noted that the north pole N moves toward or closer to the outboard section 26 and away or farther from the central section 25, while the south pole S moves toward or closer to the central section 25 and away or farther from the outboard section 27.

In FIGURE 4 I have shown a magnet assembly wherein there is a piece of magnetic material secured to the spacer 4. I have found this construction to be particularly useful for operation in the very low frequency ranges in that it augments the repulsion effects between the poles of the magnet and the poles set up in the magnetic material 23. I believe the foregoing effect is due to the fact that the material 30 reduces the effect of the air gap between the magnet and the material 23. In certain instances the material 30 may be angled to the path of relative motion.

3 This produces a smoother characteristic in the motion of the magnet.

In FIGURE 5 I have shown a single spring type pickup which is constructed similarly as the pickup of FIG- URE 1 having a housing 31, on the top part of which is a single spring 32 supporting the magnet 33 just above the coil assembly 34. The screw 35 is rotatably mounted on top of the housing. The screw engages a nut 36 which is provided with a slot which slidably engages the spring 32. As the screw is rotated by means of the knob 40, the nut is moved up and down to vary the effective vibrating length of the spring 32. Just above the magnet is mounted a frame 41 which is constructed similarly to the frame 16. This frame carries the magnetic material 42, the plan shape of which is shown in FIGURE 6. The magnetic material 42 has three discrete sections, namely, the central section 43 and the two outboard sections 44 and 45. As is shown the central section 43 is split to portions 43a and 43b, the purpose of which is to accommodate the spring 32.

I claim:

1. An inertia-type pickup having a low frequency response comprising: a housing; a permanent magnet; a coil connected with said housing and disposed below and adjacent said magnet to receive flux therefrom; means connected with said housing and supporting said magnet for vibratory motion from a neutral position to positions on opposite sides of neutral; and magnetic material connected with said housing, the magnetic material being characterized by a central section and two outboard sections to be polarized by movment of the magnet, the sections and magnet being located so that with motion of the magnet from its neutral position to one side, one pole moves toward one outboard section and away from the central section and away from the central section while the other pole moves toward the central section and away from the other outboard section.

2. An inertia-type pickup having a low frequency response comprising: a housing; two elongated strip-like, spaced-apart springs connected with the top of said housing and extending downwardly therefrom; a magnet connected with the lower end of said springs, the spring supporting said magnet for vibratory motion from a netural position to positions on either side of neutral; a coil connected with said housing and disposed below and adjacent said magnet to receive flux therefrom; and magnetic material connected with said housing and disposed over said magnet, the material being characterized by a central section extending between said springs and two outboard sections on opposite sides of said central section, the sections 3. An inertia-type pickup having a low frequency response comprising: a housing; a strip-like spring connected with the top of said housing and extending downwardly therefrom; a magnet connected with the lower end of said spring, the spring supporting the magnet for vibratory motion from a neutral position to positions on either side of neutral; a coil connected with said housing and disposed below and adjacent said magnet to receive flux therefrom; and magnetic material connected with said housing and disposed over said magnet, the material being character ized by a central section having two portions adjacent to and on opposite sides of said spring and two outboard sections on opposite sides of said central section to be polarized by movement of the magnet, the sections and magnet being located so that with motion of the magnet from its central position to one side, one pole moves toward one outboard section and away from the central section while the other pole moves toward the outboard section and away from the other outboard section, said spring extending between the two portions of said outboard section.

4. An inertia-type pickup having a low frequency response comprising: a housing; a magnet; a coil connected with said housing and disposed below and adjacent said magnet to receive flux therefrom; spring means connected with the top of said housing and extending downwardly therefrom; a magnet connected with the lower end of said spring means, the spring means supporting the magnet for vibratory motion from a neutral position to positions on either side of neutral; mechanism connected between said housing and said spring means and movable along the spring means to vary the effective vibrating length thereof; and magnetic material connected with said housing and disposed over said magnet, the material being characterized by a central section and two outboard sections on opposite sides of said central section to be polarized by movement of the magnet, the sections and magnet being located so that with motion of the magnet from its neutral position to one side, one pole moves toward one outboard section and away from the central section while the other pole moves toward the central section and away from the other outboard section.

5. A construction in accordance with claim 4 wherein said spring means comprises a single strip-like spring.

6. A construction in accordance with claim 4 wherein said spring means comprises a pair of strip-like springs.

References Cited in the file of this patent UNITED STATES PATENTS 2,429,094 Kent et al Oct. 14, 1947 2,562,983 Clewell Aug. 7, 1951 2,595,067 Flint Apr. 29, 1952 2,946,218 Karpchuk July 26, 1960 

